The process of this invention effects substitutive chlorination and crosslinking of selected polymers employing Cl.sub.2 O or HOCl.
Chlorination of polymers can produce many desirable changes in properties, and chlorinated polymers are important articles of commerce. Chlorination of polymers, particularly of hydrocarbon polymers such as polyethylene, makes them more rubbery, increases their density, renders them more resistant to air and fire, and makes shaped articles less permeable to hydrocarbons such as gasoline. Crosslinking (curing) of unsaturated polymers is an important industrial method for producing elastomers. Such crosslinking can now be effected by the method of this invention.
Dichlorine monoxide, Cl.sub.2 O, also variously known as chlorine oxide, chlorine monoxide, and dichlorine oxide, will be designated throughout this description by its formula, to avoid confusion with other chlorine oxides. Hypochlorous acid will also be designated by its formula, HOCl. Cl.sub.2 O reacts with water to give HOCl, EQU Cl.sub.2 O+H.sub.2 O.revreaction.2 HOCl
and can therefore be thought of as the anhydride of HOCl.
The Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Vol. 5, Wiley-Interscience, 1979, at pages 581 to 584, discloses two methods for making Cl.sub.2 O: (1) by reacting chlorine gas with mercuric oxide and (2) by reacting chlorine with moist sodium carbonate.
Cl.sub.2 O is a powerful chlorinating agent for organic compounds. It differs from conventional chlorinating agents such as molecular chlorine, Cl.sub.2, in that the by-product of substitutive chlorination is H.sub.2 O, not HCl. Nevertheless, as pointed out by Renard et al. in Chem Rev. 76 487 (1976), "The Chemistry of Chlorine Monoxide (Dichlorine Monoxide)" page 503, there is little evidence in the literature of efforts to develop chlorination by Cl.sub.2 O as an industrial process.
Several publications that disclose reactions of Cl.sub.2 O or HOCl with various organic compounds are as follows:
Tanner et al. in J. Am. Chem. Soc., 89, 121 (1967) disclose reaction of Cl.sub.2 O with a 10:1 molar excess of 1-chlorobutane in CCl.sub.4 at 40.degree. C. under UV irradiation to give dichlorobutanes;
Kochanny et al., in U.S. Pat. No. 3,872,176, disclose reaction of Cl.sub.2 O with 1-chloroethane alone or in CCl.sub.4 at 0.degree. to 40.degree. C. to give predominantly 1,1-dichloroethane and 1,1,1-trichloroethane;
Brooks, in U.S. Pat. No. 2,637,751, discloses reaction of HOCl with rubber to give hypochlorinated rubber in which HOCl appears to add to double bonds to give the chlorohydrin structure, --C(OH)C(Cl)--;
Burke et al., in U.S. Pat. No. 3,278,467, disclose reaction of HOCl with an isoolefin-multiolefin interpolymer to give chlorohydrin-containing interpolymers;
Landi et al., in U.S. Pat. No. 3,932,370, disclose reaction of HOCl or aqueous Cl.sub.2 with a rubber such as acrylonitrile/butadiene copolymer, styrene/butadiene copolymer, polychloroprene, or polybutadiene. Patentees do not disclose crosslinking.
Hahn et al., in CA, 84: 151182w (1976), disclose preparation of poly(N-chloroacrylamides) by chlorination of the corresponding polyacrylamides with HOCl; and
Klump et al., CA, 79: 67230z (1973), disclose preparation of N-chloro nylons by chlorinating polyamides with Cl.sub.2 O or HOCl.
It seems clear from the summaries presented above that Cl.sub.2 O has not heretofore been reacted with polymers, and that reactions of HOCl with polymers have been limited to production of N-chloro amides from polyamides and addition to carbon-carbon unsaturation in rubbers to give chlorohydrin configurations.